Wavelength selective optical switch

ABSTRACT

A wavelength selective optical switch particularly usable as a programmable N×M optical switch in a multi-wavelength communication system. The switch uses a grating that separates multi-channel optical signals into a plurality of optical channels, and combines a plurality of optical channels into multi-channel optical signals. Programmable mirrors switch each optical channel to any of a plurality of fibers coupled to the switch.

RELATED APPLICATION

This application is a divisional of prior U.S. application Ser. No.11/399,215, filed Apr. 6, 2006 now abandoned, which is a continuation ofprior U.S. application Ser. No. 10/460,899, filed Jun. 12, 2003 now U.S.Pat. No. 7,058,251, the entire contents of which are hereby incorporatedby reference herein and made a part of this specification, and claimsthe benefit of U.S. Provisional Application Nos. 60/388,358 filed Jun.12, 2002, and 60/397,944 filed Jul. 23, 2002, the disclosures of whichare also incorporated fully herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of optical communications, and moreparticularly, to a wavelength selective optical switch for use inoptical multiplexing.

BACKGROUND OF THE INVENTION

For several decades, fiber optics have been used for communication.Specifically, fiber optics are used for data transmission and othertelecommunication applications. Despite the enormous informationcarrying capacity of fiber, as compared to conventional copper cable,the high cost of installing fiber optics presents a barrier to fullimplementation of fiber optics, particular as the “last mile”, from thecentral office to residences and businesses.

One method of increasing carrying capacity without incurring additionalinstallation costs has been to multiplex multiple signals onto a singlefiber using various methods, such as time division multiplexing, wheretwo or more different signals are carried over the same fiber, eachsharing a portion of time. Another more preferred multiplexing method iswavelength division multiplexing (WDM), where two or more differentwavelengths of light are simultaneously carried over a common fiber.

Wavelength division multiplexing can separate a fiber's bandwidth intomultiple channels. Dividing bandwidth into multiple discreet channels,such as 8, 16, 40, or even as many as 160 channels, through a techniquereferred to as dense channel wavelength division multiplexing (DWDM), isa relatively lower cost method of substantially increasingtelecommunication capacity, using existing fiber optic transmissionlines. Techniques and devices are required, however, for multiplexingthe different discreet carrier wavelengths. That is, the individualoptical signals must be combined onto a common fiber-optic line or otheroptical waveguide and then later separated again into the individualsignals or channels at the opposite end or other point along thefiber-optic cable. Thus, the ability to effectively combine and thenseparate individual wavelengths (or wavelength sub-ranges) is of growingimportance to the fiber-optic telecommunications field and other fieldsemploying optical instruments.

Optical multiplexers are known for use in spectroscopic analysisequipment and for the combination or separation of optical signals inwavelength division multiplexed fiber-optic telecommunications systems.Known devices for this purpose have employed, for example, diffractiongratings, prisms and various types of fixed or tunable filters.

Approaches for selectively removing or tapping a channel, i.e.,selective wavelengths, from a main trunk line carrying multiplechannels, i.e., carrying optical signals on a plurality of wavelengthsor wavelength sub-ranges, is suggested, for example, in U.S. Pat. No.4,768,849 to Hicks, Jr. Hicks, shows filter taps, as well as the use ofgangs of individual filter taps, each employing high performance,multi-cavity dielectric pass-band filters and lenses for sequentiallyremoving a series of wavelength sub-ranges or channels from a main trunkline. The filter tap of Hicks, returns a multi-channel signal to themain trunk line as it passes the desired channel to a branch line. Oneknown demux is disclosed in Pan et al., U.S. Pat. No. 5,652,814, FIG.25. In Pan et al., the WDM input signal is cascaded through individualfilter assemblies, consisting of a fiber collimator, thin film filter,and a fiber-focusing lens. Each filter is set for a given wavelength.However, aligning the fibers for each wavelength is costly and errors inthe alignment contribute significantly to the system losses. Further,FIG. 13 of Pan et al. teaches the use of a dual fiber collimator, thinfilm filter, and a dual fiber focusing lens to selectively DROP and ADDa single wavelength or range of wavelengths. As discussed above,aligning the collimators is expensive.

Polarization dependent loss (PDL) is also a problem in WDM systembecause the polarization of the light drifts as it propagates throughthe fiber and furthermore this drift changes over time. Thus, if thereis PDL in any component, the drifting polarization will change thesignal level, which may degrade the system operation.

Other multiplexer devices may be employed to add or drop channels in WDMsystems. These systems are commonly known as optical add/dropmultiplexers, or OADM. Another OADM, disclosed by Mizrahi in U.S. Pat.No. 6,185,023, employs fiber Bragg gratings to demux and mux signals ina WDM system. This method requires optical circulators and multiplecomponents.

However, the multi channel OADM designs discussed above are notprogrammable by the end user. That is, each multiplexer is designed andmanufactured to mux (add) specific channels; or when used in reverseeach multiplexers is also designed and manufactured to demux (drop)specific channels. This limitation mandates that the optical system'sparameters be fixed before installation. Changes are not possiblewithout replacing the fixed optical multiplexers with different designedmultiplexers. This is expensive.

One known programmable OADM is discussed in Boisset et al, InternationalPublication No. WO01/13151. In Boisset et al., the desired add/dropchannel is programmed by translating a segmented filter. To achieve thistranslation however, a large mechanical mechanism is employed. A furtherlimitation to Boisset et al. is that only a single channel may be addedor dropped per device. Designers may employ multiple devices, deployedin series, and programmed as necessary to add/drop the correct channel;however, this approach requires multiple devices and has multiple pointsof failure. Furthermore, the size of such a device would be overly largeand therefore not practical for many applications where space islimited.

An OADM disclosed by Patel et al., U.S. Pat. No. 5,414,540 uses bulkgratings to demultiplex and multiplex WDM input and output signal andcompact liquid crystal switches. Because the device uses polarization toswitch the light path, the arbitrarily polarized incident beam must beconverted into a singular polarization prior to switching by the liquidcrystal. Patel teaches the use of a birefringent crystal and a Wollastonprism to separate the incident beam into two polarizations state locatedbetween the focusing lens and the liquid crystal. While the OADMdisclosed by Patel is relatively compact; it only provides 2×2 switchingfor each wavelength. There is an Input and Add channel that may beselectively sent to either the Output or Drop channel. If higherdimensionality switching is required, then additional components arerequired. The additional components require additional space, addattenuation, and add cost to the system. A 2×2 switch has four sub beamsincident on the liquid crystal (because of the conversion from anarbitrary polarized beam to a single polarization for the liquid crystalswitch) and four sub beams leaving the liquid crystal. Thus, theaperture of the lens focusing the light on the grating must be a minimumof 4× larger than that required for a single sub beam in onepolarization.

An OADM disclosed by Ranalli et al., U.S. Pat. No 6,285,500, that usesbulk gratings to demultiplex and multiplex WDM input and output signaland compact liquid crystal switches. Because the device usespolarization to switch the light path, the arbitrarily polarizedincident beam must be converted into a singular polarization prior toswitching by the liquid crystal. Ranalli teaches the use of half-waveplates and a thin film polarization beamsplitter located before the lensthat focuses light onto the liquid crystal. Because of the opticalarrangement, the aperture of the lens focusing the light on the gratingmust be a minimum of 2× larger than that required for a single sub beamin one polarization. While the OADM disclosed by Ranalli is relativelycompact; it only provides 2×2 switching for each wavelength. There is anInput and Add channel that may be selectively sent to either the Outputor Drop channel. If higher dimensionality switching is required, thenadditional components are required. The additional components requireadditional space, add attenuation, and add cost to the system.

A OADM disclosed by Patel et al., U.S. Pat. No. 6,327,019, uses bulkgratings to demultiplex and multiplex WDM input and output signal andcompact liquid crystal switches. The OADM disclosed by Patel providesfor dual 2×2 switching for each wavelength. There are two Input and twoAdd channels that may be selectively sent to either the two Output ortwo Drop channels. If higher dimensionality switching is required, thenadditional components are required. The additional components requireadditional space, add attenuation, and add cost to the system. Becauseliquid crystals use polarization to switch the light path, thearbitrarily polarized incident beam must be converted into a singularpolarization prior to switching, which doubles the required aperture ofthe lens. Thus, the dual 2×2 switch has eight sub beams incident on theliquid crystal and eight sub beams leaving the liquid crystal. Thus, theaperture of the lens focusing the light on the grating must be a minimumof 8× larger than the aperture required for single incident beam in onepolarization.

An OADM disclosed by Aksyuk, et al, U.S. Pat. No. 6,204,946 uses a bulkgrating to demultiplex and multiplex WDM input and output signal andMicro Electrical Mechanical Systems (MEMS) to provide the switching.This is another relatively compact switch, but it only provides 2×2switching for each wavelength. There is an Input and Add channel thatmay be selectively sent to either the Output or Drop channel. If higherdimensionality switching is required, then additional components arerequired. The additional components require additional space, addattenuation, and add cost to the system. Because Aksyuk uses circulatorsto separate the Input and Add channels from the Output and Dropchannels, the aperture of the lens focusing the light on the gratingmust be a minimum of 2× larger than the of a single incident beam.

Another known programmable OADM is discussed Tomlinson, U.S. Pat. No.5,960,133, uses a bulk gratings to demultiplex and multiplex WDM inputand output signal, and MEMS mirrors to switch. The OADM disclosed byTomlinson is programmable and provides for dual 2×2 switching. Tomlinsonteaches a switch that does not require the use of circulators,potentially increasing the system efficiency. However, the aperture ofthe lens focusing the light on the grating must be a minimum of(1+Sqrt[2])× larger than the of a single incident beam for a 2×2 switch.Furthermore, for a dual 2×2 without circulators, the aperture of thelens focusing the light on the grating must be a minimum of Sqrt[10]×larger than that of a single incident beam. Thus, the size and expenseof the focusing lens required grows quickly when moving from a single todual switching.

A programmable optical multiplexer/demultiplexer, disclosed by Marom etal, in US Pat. App. 02/0196520, independently assigns every inputoptical channel in a signal to depart from any desired output port,which provides the functionality of 1×N switching for every wavelength.Marom teaches the use of a bulk grating to multiplex/demultiplex WDMinput and output signal, and MEMS mirrors to switch. The demultiplexerdevice can also be operated in the reverse direction, and thus achieveprogrammable optical multiplexer functionality. However, the size andexpense of the lens required by the demultiplexer also grows linearlywith port count. A 1×5 port programmable opticalmultiplexer/demultiplexer requires a lens to focus light on the MEMsmirrors with an aperture at least 5× as large as that of a singleincident beam.

Optical gratings are a periodic structure, which diffract lightaccording to the wavelength. They can be used in either reflection ortransmission. Gratings can be produce by modulating the surface heightof a substrate or by modulating the index of refraction of a structure.

The spectral resolving power, R=λ/Δλ, of a grating is a measure of itsability to separate adjacent spectral lines, where A is averagewavelength of a line and Δλ is the limit of resolution. The theoreticalresolving power isR=Nd cos Γ(sin α+sin β)/λwhere N is the number of groves, d is the groove spacing, Γ is the anglebetween the incident light path and the plane perpendicular to thegroves, α is the angle of incidence on the grating and β is the angle ofdiffraction. If the grating is planar and the groove spacing is uniform,then the resolving power is proportional to the ruled with of thegrating, N d. Spectral resolving power is an important design parameter;the greater the resolving power the greater the optical separationbetween channels, and ultimately the channels a grating-based system canaccommodate. For low-loss transmission of OC-768 channels and a channelspacing of 100 GHz, it is preferred that the resolution be 20 GHz orfiner.

Of course, a larger grating can be employed to increase the spectralresolving power, however, that requires a combination of more physicalspace and faster or longer focal length lenses that are more expensive.Another approach has been to decrease the spacing of the gratinggrooves, d. However, the maximum theoretical efficiency of the gratingdecreases for small groove separations. When the separations between thegrooves spacing is comparable to the wavelength of light, it is possibleto get gratings that operate with high efficiency (>90%) for anyincident polarization state. As the groove spacing approaches half thewavelength of light, it is possible to get high efficiency for onlylight polarized parallel to the grooves. For even smaller groovesseparations, it is not possible to get high efficiency in eitherpolarization state. Thus, there is a practical limit to increasingspectral resolving power through decreased grating groove separations.The relationship between grating efficiency, polarization, and grooveshape is well known in the art and described in Diffraction GratingHandbook, Ch. 9, 4th Ed, Richardson Grating Laboratory, C. Palmer,(2000), which is hereby incorporated by reference. Each bulk diffractiongrating device requires a minimum number of grating grooves to achieve agiven spectral resolution. The minimum size is determined by the opticalconfiguration of the device and the grating parameters.

One desired application for optical multiplexing and demultiplexingsystems is in optical wavelength switch. An optical wavelength switchdemultiplexes optical signals, switches the signals, and then andmultiplexes to a plurality of optical ports.

The ability to switch to a number of optical ports in wavelengthswitches introduces another limiting design factor. In order to switchto a number of physical ports the size of the device must not onlyaccommodate the space needed for the ports, but the optics must alsodirect the optical signals to those ports. As the number of portsincreases the optical directing means (typically a moveable mirror) mustbe capable of directing the optical beams across a larger physical areawhere the optical ports are located. Also, as the optical beams mustexit the ports within an acceptance angle so as to be coupled into theoptical fiber, the ports must be physically located within a certainplacement angle from the directing means. As the placement angleincreases, the optical directing means generally becomes more expensiveand the insertion loss increases. An additional lens may be used tofocus the beam—however, this adds component cost and size to the device.

If the optical beams inside the device are made larger so as to increasespectral resolution the device size must increase, and in some caseslarger lenses must be used. For example, an optical switch of the typedisclosed by Marom et al. US 2002/0196520 A1, with one input port andfour output ports (1×4) might be capable of switching 64 wavelengthsspaced at 100 GHz. If the same design were used to switch 16 ports thegrating and the grating aperture would likely need to be 4× larger toaccommodate 100 GHz channels or if the grating was the same size, thesystem could switch 16 wavelength channels spaced at 400 GHz. The devicedisclosed by Marom cannot provide adequate spectral resolution for alarge number of ports and a large number of wavelengths using smallcompact lenses that are easy to manufacture.

An optical wavelength switch disclosed by Waverka et al. WO 01/37021uses a bulk diffraction grating and MEMS mirrors to provide 1×Nswitching. However, this design has a major drawback. Because the imageis translated at the spectral focal plane by the MEMS mirrors, theincident angle on the grating changes with switch position, which inturn changes the angular dispersion provided by the grating. Thus, thedevice is unable to achieve adequate spectral resolution for a largenumber of ports and a large number of wavelengths with low losses.Waverka also teaches the use of cylindrical optics to produce anelliptical beam that minimizes the size of the grating. However, becausethe cylindrical optics are used symmetrically to both collimate lightfor the grating and to focus the light on the switch array, thefootprint of the optical beam at the switch is a very high aspect ratioellipse. Thus, very long thin, hard to fabricate switches are required.

It is an object of the present invention to provide improved opticalswitching that reduce or wholly overcome some or all of the aforesaiddifficulties inherent in prior known devices. Particular objects andadvantages of the invention will be apparent to those skilled in theart, that is, those who are knowledgeable and experienced in this fieldof technology, in view of the following disclosure of the invention anddetailed description of certain preferred embodiments.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, a wavelengthselective optical switch, can establish a reconfigurable connectionbetween any two fibers from a plurality of fibers in a fiber array,independently for each optical wavelength that enters the switch. One ofa plurality of cylindrical lenses receives a first multi-channel opticalsignal from an optically coupled fiber in the array, the firstmulti-channel optical signal is directed through an anamorphic lens to agrating. The grating diffracts the first multi-channel optical signalaccording to the wavelengths of each individual optical channel, anddirects each channel through a rotationally symmetric lens that focusesthe individual optical channels near one of a plurality of programmablemirrors. Each mirror is associated with a particular individual opticalchannel. Depending upon the programmed state of the mirror, theindividual optical channel is directed to any one of the fibers in thefiber array by way of the rotationally symmetric lens, the grating, theanamorphic lens, and one of the plurality of cylindrical lenses. Bychanging the programmed state of the mirror, the individual opticalchannel may be switched to any of the fibers in the fiber array.

The invention may be used as a programmable optical demultiplexer,wherein one of the plurality of cylindrical lenses receives a firstmulti-channel optical signal from an optically coupled fiber in thearray, the first multi-channel optical signal is directed through theanamorphic lens to the grating. The grating diffracts the firstmulti-channel optical signal according to the wavelengths of eachindividual optical channel, and directs each channel through arotationally symmetric lens that focuses the individual optical channelsnear one of a plurality of programmable mirrors. Each mirror isassociated with a particular individual optical channel. Depending uponthe programmed state of the mirrors, individual optical channels aredirected to any one of the fibers in the fiber array by way of therotationally symmetric focusing lens, the grating, the anamorphic lens,and one of the plurality of cylindrical lenses. By changing theprogrammed state of the mirrors, any of the individual optical channelsmay be switched to any of the fibers in the fiber array. Further, in thecase where two or more of the individual optical channels are switchedto a single fiber, upon illuminating the grating the two or moreindividual optical channels are multiplexed into a second multi-channellight signal.

The device may also be operated in the “opposite direction” as aprogrammable multiplexer; that is two or more of the plurality ofcylindrical lenses each receives one or more different individualoptical channels from optically coupled fibers in the array, theindividual optical channels are directed through the anamorphic lens tothe grating. The grating diffracts the first multi-channel opticalsignal according to the wavelengths of each individual optical channel,and directs each channel through a rotationally symmetric lens thatfocuses the individual optical channels near one of a plurality ofprogrammable mirrors. Each mirror is associated with a particularindividual optical channel. Each of the mirrors is programmed to reflecteach of the individual optical channels to any one of the fibers in thefiber array by way of the rotationally symmetric focusing lens, thegrating, the anamorphic lens, and one of the plurality of cylindricallenses. By changing the programmed state of the mirrors, all of theindividual optical channels may be switched to any of the fibers in thefiber array.

In accordance with the first aspect of the invention, the programmedstate of the mirrors is such that a mirror connection may be establishedat any place along the fiber array. In this regard, the device can beprogrammed to establish optical connectivity, for each optical channel,between any of the fibers in the array. That is the device can operateas an N×1×M switch; directing N unique individual optical channelsreceived from one fiber in a fiber array to any of the M fibers in thefiber array.

The device may also direct two or more individual optical channelscentered at the same wavelength and received from two or more fibers inthe fiber array to other fibers in the array. However, the switchingmatrix is more restrictive as the same mirror is used for the directionof all the individual optical channels centered at the same wavelength.In this manner, each of the individual optical channels centered at thesame wavelength are directed to the fiber in the fiber array that isopposite the mirror's connection. For example, consider a nine portdevice coupled to a nine fiber array (the consecutive fibers numbered 1through 9) which receives a first individual optical channel centered atwavelength x on port 1, and receives a second individual optical channelcentered at wavelength x on port 2. If the corresponding mirrorconnection for wavelength x is set such that the light at wavelength xentering the switch from fiber 3 also leaves from fiber 3, then thefirst individual optical channel at wavelength x will be directed tofiber 5, and the second at wavelength x to fiber 4. In this manner, thedevice does not operate as an N×1×M switch, but still provides numerousswitching options. Such options will be clear to one skilled in the art.

In accordance with a second aspect of the invention, a wavelengthselective optical switch, can establish a reconfigurable connectionbetween any two fibers from a plurality of fibers in a fiber array,independently for each optical wavelength that enters the switch. One ofa plurality of cylindrical lenses receives a first multi-channel opticalsignal from an optically coupled fiber in the array, the firstmulti-channel optical signal is directed through an anamorphic lens, toa beam splitter. The beam splitter separates light that is s-polarizedfrom light that is p-polarized, and directs both out of the beamsplitter through a first and second quarter waveplate. The s-polarizedlight illuminates a first grating, and the p-polarized light illuminatesa second grating. The gratings diffract the respective s-polarized andp-polarized first multi-channel optical signal according to thewavelengths of each individual optical channel, and direct therespective s-polarized and p-polarized light of each individual opticalchannel back through the quarter waveplate into the beam splitter, whichrecombines the s-polarized and p-polarized light of each channel anddirects the individual optical channels through a rotationally symmetriclens that focuses the individual optical channels near one of aplurality of programmable mirrors. Each mirror is associated with aparticular individual optical channel. Depending upon the programmedstate of the mirror, the individual optical channel is directed to anyone of the fibers in the fiber array by way of the rotationallysymmetric lens, the beam splitter, waveplates and gratings, the beamsplitter, anamorphic lens, and one of the plurality of cylindricallenses. By changing the programmed state of the mirror, the individualoptical channel may be switched to any of the fibers in the fiber array.

The device may also be operated in the “opposite direction” as aprogrammable multiplexer; that is two or more of the plurality ofcylindrical lenses each receives one or more different individualoptical channels from optically coupled fibers in the array, theindividual optical channels are directed through the anamorphic lens tothe beam splitter. The beam splitter separates the s-polarized andp-polarized states and directs each to the first and second gratings.The gratings diffracts the first multi-channel optical signal accordingto the wavelengths of each individual optical channel, and directs eachchannel back through the beam splitter recombining the s-polarized andp-polarized states, and directing the individual optical channel throughthe rotationally symmetric lens that focuses the individual opticalchannels near one of a plurality of programmable mirrors. Each mirror isassociated with a particular individual optical channel. Each of themirrors is programmed to reflect each of the individual optical channelsto any one of the fibers in the fiber array. By changing the programmedstate of the mirrors, all of the individual optical channels may beswitched to any of the fibers in the fiber array.

In accordance with the second aspect of the invention, the programmedstate of the mirrors is such that a mirror connection may be establishedat any place along the fiber array. In this regard, the device can beprogrammed to establish optical connectivity, for each optical channel,between any of the fibers in the array. That is the device can operateas an N×1×M switch; directing N unique individual optical channelsreceived from one fiber in a fiber array to any of the M fibers in thefiber array.

The device may also direct two or more individual optical channelscentered at the same wavelength and received from two or more fibers inthe fiber array to other fibers in the array. However, the switchingmatrix is more restrictive as the same mirror is used for the directionof all the individual optical channels centered at the same wavelength.In this manner, each of the individual optical channels centered at thesame wavelength are directed to the fiber in the fiber array that isopposite the mirror's connection. For example, consider a nine portdevice coupled to a nine fiber array (the consecutive fibers numbered 1through 9) which receives a first individual optical channel centered atwavelength x on port 1, and receives a second individual optical channelcentered at wavelength x on port 2. If the corresponding mirrorconnection for wavelength x is set such that the light at wavelength xentering the switch from fiber 3 also leaves from fiber 3, then thefirst individual optical channel at wavelength x will be directed tofiber 5, and the second at wavelength x to fiber 4. In this manner, thedevice does not operate as an N×1×M switch, but still provides numerousswitching options. Such options will be clear to one skilled in the art.

In accordance with several aspects of the invention one or more waveplates may be employed to reduce polarization dependent loss (PDL). Theone or more wave plates rotates the polarization so that light that iss-polarized on a first pass is p-polarized on a second pass and there isno net polarization dependent loss (PDL) for light traveling through thedevice. Similarly, a polarization converter such as a rutile crystal maybe used in combination with wave plates to reduce PDL.

In accordance with several aspects of the invention, the grating orgratings may operate at or near Littrow to increase the diffractionefficiency. In accordance with several aspects of the invention one ormore transmission gratings may be employed. In accordance with severalaspects of the invention, a beam displacer made of birefringent crystalsor multi-layer coated polarization beamsplitters may be employed toseparate and combine optical beams. Different aspects of the inventionmay also be employed together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 1(B) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 1(C) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 2(A) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 2(B) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 2(C) is a perspective view of a first embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 3(A) is a perspective view of a second embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 3(B) is a perspective view of a second embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 3(C) is a perspective view of a second embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 4 is a perspective view of a second embodiment of a wavelengthselective optical switch detailing the optical polarization states atvarious locations within the device.

FIG. 5(A) is a perspective view of a third embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 5(B) is a perspective view of a third embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 5(C) is a perspective view of a third embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 6(A) is a perspective view of a fourth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 6(B) is a perspective view of a fourth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 6(C) is a perspective view of a fourth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 7(A) is a perspective view of a fifth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 7(B) is a perspective view of a fifth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 7(C) is a perspective view of a fifth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 8(A) is a perspective view of a sixth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 8(B) is a perspective view of a sixth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 8(C) is a perspective view of a sixth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 8(D) is a perspective view of a sixth embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 9(A) is a perspective view of a seventh embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 9(B) is a perspective view of a seventh embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 9(C) is a perspective view of a seventh embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 9(D) is a perspective view of a seventh embodiment of a wavelengthselective optical switch detailing the optical paths through the device.

FIG. 10 is a perspective view of a seventh embodiment of a wavelengthselective optical switch detailing the optical polarization states atvarious locations within the device.

DETAILED DESCRIPTION OF THE INVENTION

The wavelength selective optical switch of the invention has numerousapplications, including use in fiber optic telecommunications systems.For purposes of illustration, the embodiments described below detaildemultiplexing, switching, and multiplexing in a multi-channel fiberoptic telecommunication systems. Exemplary references to an opticalchannel, or simply to a channel, should be understood to mean an opticalsignal with a centered wavelength and an upper and lower wavelength.Channel spacing is measured from the center of the first channel to thecenter of an adjacent channel.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 1(A), FIG. 1(B), and FIG. 1(C). FIG.1(A), FIG. 1(B), and FIG. 1(C) detail different views of the samedevice. It is of note that while only two channels are used in thisexample, a substantially larger number of channels and optical ports maybe employed. The wavelength selective optical switch allows fordemultiplexing, multiplexing and switching separate optical channels toany one of a plurality of optical ports. The wavelength selectiveoptical switch of FIG. 1 may be dynamically programmed to demultiplex,multiplex and switch any combination of wavelengths to any of aplurality of optical ports.

A first embodiment of the wavelength selective optical switch device ofFIG. 1(A), FIG. 1(B), and FIG. 1(C) comprises a Cylindrical Lens Array103 optically coupled to an Input Fiber 101, an Anamorphic Lens 105, aGrating 109, a Rotationally Symmetric Lens 111, a Array of ProgrammableMirrors 113, a first Output Fiber 101-a, and a second Output Fiber101-b. A cylindrical lens has at least one surface that is formed like aportion of a cylinderz(x)=cx^2/{1+Sqrt[1−(1+k)c^2x^2]}+Ax^4+Bx^6+Cx^8+Dx^10where z(x) is the sag, c is the curvature at the pole of the surface, xis the distance from the center of the lens along the x-axis, k is theconic constant, and A, B, C, D are aspheric coefficients. Note that inthis case that sag is independent of the y-coordinate. An anamorphiclens, usually having one more cylindrical surfaces, has a differentmagnification along mutually perpendicular meridians. The device of FIG.1 may be mounted within an enclosure optimized for optical transmission,including a gas-filled enclosure, or the like.

Cylindrical Lens Array 103, Anamorphic Lens 105, and RotationallySymmetric Lens 111 may be comprised of multiple lens elements. It iswell known in the art that lenses may be comprised of multiple lenselements to achieve a particular optical performance.

The Array of Programmable Mirrors 113 is responsible for steeringoptical signals. However, other beam steering devices, such as a liquidcrystal or the like, may also be employed. Cassarly et-al teach one suchliquid crystal beam steering device in U.S. Pat. No. 5,107,357, which isfully incorporated by reference herein. It will be clear to one skilledin the art that beam steering devices may be used in any of thedescribed embodiments. In addition, whichever means is employed forsteering the optical signals may also steer the optical signals in morethan one axis. This permits, among other things, the steering of opticalsignals from one port to another port without directing the opticalsignal to a third port. This allows one port in the system to be steeredto another port without interfering with any other ports that might bein use at the time.

A prism may optionally be used in any embodiment of the system.Temperature changes cause grating to expand and contract. As gratingsexpand and contract the wavelength-sized gradations that causediffraction increase and decrease causing a change in the diffractionangle from a grating. As the temperature changes, the refractive indexof the prism changes, which in turn, changes the dispersion of theprism. Accordingly, a prism may be used to balance the thermal affectson Grating 109. When the prism and Grating 109 are properly designed andconfigured the effects of temperature on the system are greatly reduced.However, some embodiments of the system do not contain a prism.

Quarter-wave plate (QWP) 107 may also be employed between theRotationally Symmetric Lens 111 and grating 109 to reduce polarizationdependent loss (PDL) in the system. The QWP 107 oriented at 45 deg tothe grating lines rotates the polarization so that light that iss-polarized at the grating on the first pass is p-polarized on thesecond pass and there is no net polarization dependent loss (PDL) forlight traveling between the Input Fiber 101 and any of the Output Fibers(101-a through 101-b).

A multi-channel light signal 115 enters the device through the InputFiber 101, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 103. The Cylindrical Lens on the Cylindrical LensArray 103 collimates the multi-channel light signal 115 in the x-axisand directs it through the Anamorphic Lens 105. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Anamorphic Lens 105 collimates and focuses the multi-channel lightsignal 115 in the y-axis and directs it through QWP 107, and ontoGrating 109. The cylindrical and anamorphic lenses produce a beam withan elliptical footprint on the grating. The major axis of the ellipse isperpendicular to the grooves so that the spectral resolution ismaximized, while the overall size of the grating is less than that if aconventional rotationally symmetric collimating lens were used.

The Grating 109 diffracts the individual Channels 117 and 119 of themulti-channel light signal 115 (hereafter channels) towards theRotationally Symmetric Lens 111. The Rotationally Symmetric Lens 111 ispreferably telecentric, so that the central ray, or chief ray, of eachchannel is parallel at the MEMS plane. This minimizes the tilt requiredby the MEMS mirrors. In a telecentric lens, the aperture stop is locatedat the front focus of the lens, resulting in the exit pupil being atinfinity. The Rotationally Symmetric Lens 111 focuses the Channels 117and 119, near the Programmable Mirror on the Mirror Array 113. Morespecifically, Rotationally Symmetric Lens 111 focuses Channel 117 nearthe Programmable Mirror associated with Channel 117, and focuses channel119 near the Programmable Mirror associated with channel 119. Byfocusing the channels in two axes the optical beam size is reduced andthe size of the Programmable Mirrors 117 and 119 and Mirror Array 113may be reduced.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the two of Output Fibers 101-a or101-b. In this regard, each the channel is reflected back through theRotationally Symmetric Lens 111 which collimates the channels towardGrating 109. Grating 109 multiplexes the channels switched to the sameoutput fiber and diffracts the resulting beam toward that output fiber.In the presently detailed case of FIG. 1, the Programmable Mirrors areprogrammed so as to switch Channel 117 to Output Fiber 101-a and Channel119 to Output Fiber 101-b. Therefore, Channel 117 is reflected from itsProgrammable Mirror through Rotationally Symmetric Lens 111 whichcollimates the Channel towards Grating 109. Grating 109 diffractsChannel 117 through QWP 107 and Anamorphic Lens 105. Anamorphic Lens 105focuses Channel 117 in the y-axis toward Cylindrical Lens 103, whichfocuses Channel 117 in the x-axis and into Output Fiber 101-a.Similarly, Channel 119 is reflected from its Programmable Mirror throughRotationally Symmetric Lens 111 which collimates the Channel towardsGrating 109. Grating 109 diffracts Channel 119 through QWP 107 andAnamorphic Lens 105. Anamorphic Lens 105 focuses Channel 119 in they-axis toward Cylindrical Lens 103, which focuses Channel 119 in thex-axis and into Output Fiber 101-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 101-a and 101 b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 117 or Channel 119may be switched to either Output Fiber 101-a or 101-b by simply changingthe angle of reflection of the associated Programmable Mirror. In thisregard, the system may be scaled to accommodate both a large number ofOutput Fibers, but also a large number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, receiving an opticalChannel 117 via Port 101-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port101.

Turning next to FIG. 2(A), FIG. 2(B), and FIG. 2(C). FIG. 2(A), FIG.2(B), and FIG. 2(C) detail different views of the same device. Thisembodiment operates similarly to the embodiment detailed FIG. 1(A), FIG.1(B), and FIG. 1(C) above; however, it further employs one or morepolarization converters. The operation of a polarization converter iswell known in the art. Ducellier teaches one such polarization converterin U.S. Pat. No. 6,411,409, which is fully incorporated by referenceherein. As explained, a birefringent crystal beam displacer is orientedin such a way as to separate the input light into two sub-beams withs-polarizations and p-polarizations. A half-wave plate (HWP) covers thep-polarized sub-beam to convert it to s-polarization. Thus, the lightleaves the polarization converter with a larger beam, but it is entirelyin the s-polarization, which has the highest diffraction efficiency atthe high frequency gratings. The birefringent crystal beam displacerpreferably uses a uniaxial birefringent crystals such as calcite(CaCO3), yrttrium orthovandate (YV04) or rutile (TiO2) to separate thebeams. Another common polarization converter uses a polarization beamsplitter and a waveplate. The waveplate is usually a single half-waveplate oriented at 45 degrees with respect to the groove axis positionedin the path of one of the two sub-beams.

The embodiment of present invention detailed in FIG. 2(A), FIG. 2(B),and FIG. 2(C) employs one or more polarization converters. PolarizationConverter 201 is positioned in the optical path between Input Fiber 101and the Diffraction Grating 109 and converts multi-channel light signal115 to entirely s-polarized light. Accordingly, when the larger beamwidth and entirely s-polarized multi-channel light signal 115,illuminates Grating 109, it does so at the highest diffractionefficiency.

Optional Polarization Converter 203, operated in the opposite directionas Polarization Converter 201, is positioned in the optical path betweenDiffraction Grating 109 and the Array of Programmable Mirrors 113.Polarization Converter 203 re-converts the entirely s-polarized lightback to both p-polarized and s-polarized light. Additionally, the sizeof the combined p-polarized and s-polarized beam leaving thepolarization converter is smaller than that of the entirely s-polarizedsub-beam entering the converter. This reduces the footprint of the beamat the MEMS mirrors and which enables the use of a smaller size of theMEMS mirror without incurring additional insertion losses. It will beclear to one skilled in the art that there are many ways to ensure thatthe grating efficiency is maximized by illuminating only withs-polarized light.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 3(A), FIG. 3(B), and FIG. 3(C). FIG.3(A), FIG. 3(B), and FIG. 3(C) detail different views of the samedevice. It is of note that while only two channels are used in thisexample, a substantially larger number of channels and optical ports maybe employed. This embodiment allows for demultiplexing, multiplexing andswitching separate optical channels to any one of a plurality of opticalports. This embodiment may be dynamically programmed to demultiplex,multiplex and switch any combination of wavelengths to any of aplurality of optical ports.

A Littrow grating is a grating that operates at or near Littrow. Littrowis a special, but common case, in which the angle of incidence of thelight on the grating is equal to the angle of diffraction] for which thegrating equation becomes:ml=2d sin(a)where a is the incident angle (same as the diffracted angle), m is thegrating order, I is the wavelength, and d is the grating groove spacing.For a reflection grating, rays diffract off the grating back toward thedirection from which they originated. In one embodiment, the grating isused near the Littrow condition. Further, using the gratings near theLittrow condition takes advantage of the high diffraction efficiencynear the Littrow condition.

The embodiment of the wavelength selective optical switch, detailed inFIG. 3(A), FIG. 3(B), and FIG. 3(C), comprises a Cylindrical Lens Array303 optically coupled to an Input Fiber 301, an Anamorphic Lens 305, aPolarization Beam Splitter (PBS) 307, Littrow Gratings 311 and 313, QWP315, QWP 317, QWP 319, a Rotationally Symmetric Lens 321, a Array ofProgrammable Mirrors 323, a first Output Fiber 301-a, and a secondOutput Fiber 301-b. The device of FIG. 3 may be mounted within anenclosure optimized for optical transmission, including a gas-filledenclosure, or the like. The cylindrical and anamorphic lenses produce abeam with an elliptical footprint on the grating. The major axis of theellipse is perpendicular to the grooves so that the spectral resolutionis maximized, while the overall size of the grating is less than that ifa conventional rotationally symmetric collimating lens were used.

Anamorphic Lens 305 and Rotationally Symmetric Lens 311 may be comprisedof multiple lens elements. It is well known in the art that lenses maybe comprised of multiple lens elements to achieve a particular opticalperformance.

A prism may optionally be used in any embodiment of the system.Temperature changes cause grating to expand and contract. As gratingsexpand and contract the wavelength-sized gradations that causediffraction increase and decrease causing a change in the diffractionangle from a grating. As the temperature changes, the refractive indexof the prism changes, which in turn, changes the dispersion of theprism. Accordingly, a prism may be used to balance the thermal affectson Gratings 311 and 313. When the prism and Gratings 311 and 313 areproperly designed and configured the effects of temperature on thesystem are greatly reduced. However, some embodiments of the system donot contain a prism.

QWP 319 may also be employed to reduce polarization dependent loss (PDL)in the system. QWP 319 oriented at 45 degrees to the grating linesrotates the polarization of light, so that light that is s-polarized atthe grating on the first pass is p-polarized on the second pass. The netresult is no polarization dependent loss (PDL) for light travelingbetween the Input Fiber 301 and any of the Output Fibers 301-a and301-b.

A multi-channel light signal 315 enters the device through the InputFiber 301, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 303. The Cylindrical Lens on the Cylindrical LensArray 303 collimates the multi-channel light signal 315 in the x-axisand directs it through the Anamorphic Lens 305. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Anamorphic Lens 305 collimates and focuses the multi-channel lightsignal 315 in the y-axis and directs into the PBS 307. The PBS separatesmulti-channel light signal 315 into its s-polarized and p-polarizedstates.

Turning briefly to FIG. 4., the polarization states of multi-channellight signal 315 are described in detail. Multi-channel light signal 325enters the PBS 307 and strikes upon the Beam Splitting Surface 309. Thes-polarized optical component reflects off of Beam Splitting Surface 309and exits the PBS 307. This s-polarized optical component 325-S passesthrough QWP 315, which converts the polarization state to right-circular325-RC, and illuminates Littrow Grating 313. Littrow Grating 313diffracts the individual channels of light (now left-circular polarizedafter diffracting of Littrow Grating 313) back through QWP 315 whichconverts their polarization to a p-polarized state 325-P, and into thePBS 309. Because these individual channels are now p-polarized theytransmit through Beam Splitting Surface 309 and exit the PBS 307,passing though QWP 319 that converts the polarization states fromp-polarized to left-circular 325-LC.

In much the same fashion as described above with the s-polarized opticalcomponent, the p-polarized optical component transmits through BeamSplitting Surface 309, exits PBS 307, and passes though QWP 317 whichconverts the polarization state from p-polarized to left-circular, andilluminates Littrow Grating 311. Littrow Grating 311 diffracts theindividual channels of light (now right-circular polarized) back throughQWP 317 that converts their polarization to an s-polarized state, andinto the PBS 309. The s-polarized optical component reflects off of BeamSplitting Surface 309 and exits the PBS 307 passing though QWP 319 thatconverts the polarization states from s-polarized to right-circular325-RC.

Turning again to FIG. 3(A), FIG. 3(B), and FIG. 3(C), Grating 313 and311 diffracts the individual Channels 327 and 329 of the multi-channellight signal 325 (hereafter channels) through the PBS 307 and towardsthe Rotationally Symmetric Lens 321. The Rotationally Symmetric Lens 321is preferably telecentric, so that the central ray, or chief ray, ofeach channel is parallel at the MEMS plane. This minimizes the tiltrequired by the MEMS mirrors. In a telecentric lens, the aperture stopis located at the front focus of the lens, resulting in the exit pupilbeing at infinity. The Rotationally Symmetric Lens 321 focuses Channels317 and 319 in both the x-axis and z-axis, near the Programmable Mirroron the Mirror Array 313. More specifically, Rotationally Symmetric Lens321 focuses Channel 327 near the Programmable Mirror associated withChannel 327, and focuses channel 329 near the Programmable Mirrorassociated with channel 329. By focusing the channels in both the x-axisand z-axis, the optical beam size is reduced.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the two of Output Fibers 301-a or301-b. In this regard, each the channel is reflected back through theRotationally Symmetric Lens 321 which collimates the channels in boththe x-axis and z-axis and directs the channels through PBS 307 and ontoGratings 311 and 313. Gratings 311 and 313 multiplex the channelsswitched to the same output fiber and diffracts the resulting beamtoward that output fiber. In the presently detailed case of FIG. 3, theProgrammable Mirrors are programmed so as to switch Channel 327 toOutput Fiber 301-a and Channel 329 to Output Fiber 301-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 301-a and 301 b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 317 or Channel 319may be switched to either Output Fiber 301-a or 301-b by simply changingthe angle of reflection of the associated Programmable Mirror. In thisregard, the system may be scaled to accommodate both a large number ofOutput Fibers, but also a large number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, by receiving an opticalChannel 327 via Port 301-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port301.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 5(A), FIG. 5(B), and FIG. 5(C). FIG.5(A), FIG. 5(B), and FIG. 5(C) detail different views of the samedevice. It is of note that while only two channels are used in thisexample, a substantially larger number of channels and optical ports maybe employed. The wavelength selective optical switch allows fordemultiplexing, switching separate optical channels, and multiplexing toany one of a plurality of optical ports. The wavelength selectiveoptical switch of FIG. 5 may be dynamically programmed to demultiplex,multiplex and switch any combination of wavelengths to any of aplurality of optical ports.

The embodiment of the wavelength selective optical switch device of FIG.5(A), FIG. 5(B), and FIG. 5(C) comprises a Cylindrical Lens Array 503optically coupled to an Input Fiber 501, an Anamorphic Lens 505, atransmissive Grating 513 operating near Littrow, a RotationallySymmetric Lens 521, a Array of Programmable Mirrors 523, a first OutputFiber 501-a, and a second Output Fiber 501-b. The device of FIG. 5 maybe mounted within an enclosure optimized for optical transmission,including a gas-filled enclosure, or the like. The cylindrical andanamorphic lenses produce a beam with an elliptical footprint on thegrating. The major axis of the ellipse is perpendicular to the groovesso that the spectral resolution is maximized, while the overall size ofthe grating is less than that if a conventional rotationally symmetriccollimating lens were used.

Anamorphic Lens 505 and Rotationally Symmetric Lens 521 may be comprisedof multiple lens elements. It is well known in the art that lenses maybe comprised of multiple lens elements to achieve a particular opticalprescription.

A prism may optionally be used in any embodiment of the system.Temperature changes cause grating to expand and contract. As gratingsexpand and contract the wavelength-sized gradations that causediffraction increase and decrease causing a change in the diffractionangle from a grating. As the temperature changes, the refractive indexof the prism changes, which in turn, changes the dispersion of theprism. Accordingly, a prism may be used to balance the thermal affectson Grating 513. When the prism and Grating 513 are properly designed andconfigured the effects of temperature on the system are greatly reduced.However, some embodiments of the system do not contain a prism.

The embodiment of present invention detailed in FIG. 5(A), FIG. 5(B),and FIG. 5(C) employs one or more polarization converters. PolarizationConverter 502 is positioned in the optical path between Input Fiber 501and the Grating 513 and converts multi-channel light signal 525 toentirely s-polarized light. Accordingly, when the larger beam width andentirely s-polarized multi-channel light signal 525, illuminates Grating513, it does so at the highest diffraction efficiency.

Optional Polarization Converter 524, operated in the opposite directionas Polarization Converter 502, is positioned in the optical path betweenGrating 513 and the Array of Programmable Mirrors 523. PolarizationConverter 524 re-converts the entirely s-polarized light back to bothp-polarized and s-polarized light. Additionally, the size of thecombined p-polarized and s-polarized beam leaving the polarizationconverter is smaller than that of the entirely s-polarized sub-beamentering the converter. This reduces the footprint of the beam at theMEMS mirrors and which enables the use of a smaller size of the MEMSmirror without incurring additional insertion losses.

A multi-channel light signal 525 enters the device through the InputFiber 501, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 503. The Cylindrical Lens on the Cylindrical LensArray 503 collimates the multi-channel light signal 525 in the x-axisand directs it through the Anamorphic Lens 505. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Anamorphic Lens 505 collimates and focuses the multi-channel lightsignal 525 in the y-axis and directs it through Grating 513. Thecylindrical and anamorphic lenses produce a beam with an ellipticalfootprint on the grating. The major axis of the ellipse is perpendicularto the grooves so that the spectral resolution is maximized, while theoverall size of the grating is less than that if a conventionalrotationally symmetric collimating lens were used.

The Grating 513 diffracts the individual Channels 527 and 529 of themulti-channel light signal 525 (hereafter channels) through QWP 519 andtowards the Rotationally Symmetric Lens 521. The Rotationally SymmetricLens 521 focuses the Channels 527 and 529, in both the x-axis andz-axis, near the Programmable Mirror on the Mirror Array 523. Morespecifically, Rotationally Symmetric Lens 521 focuses Channel 527 nearthe Programmable Mirror associated with Channel 527, and focuses channel529 near the Programmable Mirror associated with channel 529. Byfocusing the channels in both the x-axis and z-axis, the optical beamsize is reduced and the size of the Programmable Mirrors and MirrorArray 523 may be reduced. Further, the focal length may be reducedthereby compacting the device.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the two of Output Fibers 501-a or501-b. In this regard, each the channel is reflected back through theRotationally Symmetric Lens 521 which collimates the channels in boththe x-axis and z-axis and directs the channels through Grating 513.Grating 513 multiplexes the channels switched to the same output fiberand diffracts the resulting beam toward that output fiber. In thepresently detailed case of FIG. 5, the Programmable Mirrors areprogrammed so as to switch Channel 527 to Output Fiber 501-a and Channel529 to Output Fiber 501-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 501-a and 501 b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 527 or Channel 529may be switched to either Output Fiber 501-a or 501-b by simply changingthe angle of reflection of the associated Programmable Mirror. In thisregard, the system may be scaled to accommodate both a large number ofOutput Fibers, but also a large number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, by receiving an opticalChannel 527 via Port 501-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port501.

A seventeen port grating-based optical switch for sixty four 100 GHzspaced channels, employing one embodiment of the invention, is detailedin FIG. 6(A), FIG. 6(B), and FIG. 6(C). FIG. 6(A), FIG. 6(B), and FIG.6(C) detail different views of the same device. For clarity, in FIG.6(A), FIG. 6(B), and FIG. 6(C), only the center and extreme ports, and 2optical channels, are depicted. The wavelength selective optical switchallows for demultiplexing, switching separate optical channels, andmultiplexing to any one of a plurality of optical ports. The wavelengthselective optical switch of FIG. 6 may be dynamically programmed todemultiplex, switch, and multiplex any combination of channels to any ofa plurality of optical ports.

The embodiment of the wavelength selective optical switch device of FIG.6(A), FIG. 6(B), and FIG. 6(C) comprises a Cylindrical Lens Array 603optically coupled to an Input Fiber 601, a Cylindrical Lens 605, a prism607, a transmission Grating 609 operating near Littrow, a RotationallySymmetric Lens 611, an Array of Programmable Mirrors 613, a first OutputFiber 601-a, and a second Output Fiber 601-b. The device of FIG. 6 maybe mounted within an enclosure optimized for optical transmission,including a gas-filled enclosure, or the like. The cylindrical andanamorphic lenses produce a beam with an elliptical footprint on thegrating. The major axis of the ellipse is perpendicular to the groovesso that the spectral resolution is maximized, while the overall size ofthe grating is less than that if a conventional rotationally symmetriccollimating lens were used.

Cylindrical Lens 605 and Rotationally Symmetric Lens 611 are bothcomprised of multiple lens elements. It is well known in the art thatlenses may be comprised of multiple lens elements to reduce the lensaberrations over a large range of frequencies (6.4 THz), operatingtemperatures (−20° C. to 70° C.), and field of view. Cylindrical Lens605 and Rotationally Symmetric Lens 611 have numeric apertures of 0.2and 0.235, respectively. Table 1 lists the optical prescription for thewavelength selective optical switch in CODE V format.

TABLE 1 Optical Prescription for seventeen port grating-based opticalswitch OBJ: RDY THI RMD GLA INFINITY 3.146570 1: INFINITY 0.450000SILICON_SPECIAL 2: INFINITY 0.000000 RDX: −8.10984 Lens spacing:1.3347E+00 A: 1.2682E−03 3: INFINITY 0.453430 AIR 4: −3.30747 2.919365SF11_SCHOTT CYL: RDX: INFINITY 5: −3.74895 11.188256 AIR CYL: RDX:INFINITY 6: −39.82847 2.000000 SF15_SCHOTT CYL: RDX: INFINITY 7: 8.252893.069427 NBAK1_SCHOTT CYL: RDX: INFINITY 8: −7.03286 0.214935 AIR CYL:RDX: INFINITY 9: −6.44129 2.000000 NBK10_SCHOTT CYL: RDX: INFINITY 10:9.62630 2.938672 NSK2_SCHOTT CYL: RDX: INFINITY 11: −15.90151 0.328897AIR CYL: RDX: INFINITY 12: INFINITY 3.000000 SF14_SCHOTT SLB: “prism”13: INFINITY 3.000000 AIR XDE: 0.000000 YDE: 0.000000 ZDE: 0.000000 ADE:15.219671 BDE: 0.000000 CDE: 0.000000 14: INFINITY 0.000000 AIR XDE:0.000000 YDE: 0.000000 ZDE: 0.000000 ADE: 0.1e21 BDE: 0.000000 CDE:0.000000 15: INFINITY 0.000000 AIR XDE: 0.000000 YDE: −2.190327 ZDE:17.000000 GLB G12 ADE: −76.238409 BDE: 0.000000 CDE: 0.000000 16:INFINITY 2.000000 SILICA_SPECIAL STO: INFINITY 2.000000 SILICA_SPECIALSLB: “grt” GL2: AIR GRT: GRO: −1.000000 GRS: 0.000909 GRX: 0.000000 GRY:1.000000 GRZ: 0.000000 18: INFINITY 2.000000 AIR 19: INFINITY 10.626347AIR XDE: 0.000000 YDE: −3.824794 ZDE: 0.000000 ADE: −56.872509 BDE:0.000000 CDE: 0.000000 20: 40.02527 5.798156 NLASF31_SCHOTT SLB: “foc”21: −510.83375 5.947632 NLAK10_SCHOTT 22: 127.58156 1.702233 AIR 23:19.84076 4.276553 NSF1_SCHOTT 24: 25.60107 4.125666 SF1_SCHOTT 25:12.99810 11.900816 AIR 26: −21.31335 2.894729 NLAK10_SCHOTT 27: 68.5446212.995558 NLASF31_SCHOTT 28: −31.91252 6.790847 AIR 29: 43.8183512.994567 SF57_SCHOTT 30: −47.90572 12.994310 SFL57_SCHOTT 31: 138.805965.065914 AIR 32: INFINITY 0.000000 XDE: 0.000000 YDE: 0.000000 ZDE:0.000000 DAR ADE: 0.371634 BDE: 0.000000 CDE: 0.000000 IMG: INFINITY0.000000

The embodiment of present invention detailed in FIG. 6(A), FIG. 6(B),and FIG. 6(C) employs a Volume Holographic Grating 609 with 1100grooves/mm made on a substrate with low coefficient of thermalexpansion, such as fused silica. Because this grating has poorefficiency in the p-polarization, the s- and p-polarization are split(not shown) and the s-polarization is switched by the optics shown inFIG. 6(A), FIG. 6(B), and FIG. 6(C). The p-polarization is rotated by90°, so that it is s-polarized, and sent through a set of optics thatare identical to the s-polarized optics. This technique of splitting thetwo polarizations and running each through an identical set of optics isknown as polarization diversity.

Prism 607 is employed to compensate for changes in the grating groovespacing with temperature. As gratings expand and contract thewavelength-sized gradations that cause diffraction increase and decreasecausing a change in the diffraction angle from a grating. As thetemperature changes, the refractive index of the prism changes, which inturn, changes the dispersion of the prism. Accordingly, prism 607 isused to balance the thermal affects on Grating 609. When Prism 607 andGrating 609 are properly designed and configured the effects oftemperature on the system are greatly reduced. Prism 607 is preferablemade of a glass with a large change in the optical path length withtemperature, such as SF14 by Schott, to minimize the prismatic powerrequired.

A multi-channel light signal 615 enters the device through the InputFiber 601, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 603. The Cylindrical Lens on the Cylindrical LensArray 603 collimates the multi-channel light signal 615 in the x-axisand directs it through the Anamorphic Lens 605. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Cylindrical Lens 605 collimates and focuses the multi-channel lightsignal 615 in the y-axis and directs it through Grating 609.

The Grating 609 diffracts the individual Channels 617 and 619 (hereafterchannels) of the multi-channel light signal 615 towards the RotationallySymmetric Lens 611. The Rotationally Symmetric Lens 611 focuses theChannels 617 and 619, near the Programmable Mirror on the Mirror Array613. More specifically, Rotationally Symmetric Lens 611 focuses Channel617 near the Programmable Mirror associated with Channel 617, andfocuses channel 619 near the Programmable Mirror associated with channel619. By focusing the channels, the optical beam size is reduced and thesize of the Programmable Mirrors and Mirror Array 613 may be reduced.Further, the focal length may be reduced thereby compacting the device.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the Output Fibers 601-a or 601-b.In this regard, each the channel is reflected back through theRotationally Symmetric Lens 611 which collimates the channels anddirects the channels through Grating 609. Grating 609 multiplexes thechannels switched to the same output fiber and diffracts the resultingbeam toward that output fiber. In the presently detailed case of FIG. 6,the Programmable Mirrors are programmed so as to switch Channel 617 toOutput Fiber 601-a and Channel 619 to Output Fiber 601-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 601-a and 601 b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 617 or Channel 619may be switched to either Output Fiber 601-a or 601-b by simply changingthe angle of reflection of the associated Programmable Mirror. In thisregard, the system supports both a large number of Output Fibers, and alarge number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, by receiving an opticalChannel 617 via Port 601-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port601.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 7(A), FIG. 7(B), and FIG. 7(C). FIG.7(A), FIG. 7(B), and FIG. 7(C) detail different views of the samedevice. It is of note that while only two channels are used in thisexample, a substantially larger number of channels and optical ports maybe employed. This embodiment allows for demultiplexing, multiplexing andswitching separate optical channels to any one of a plurality of opticalports. This embodiment may be dynamically programmed to demultiplex,multiplex and switch any combination of wavelengths to any of aplurality of optical ports.

The embodiment of the wavelength selective optical switch, detailed inFIG. 7(A), FIG. 7(B), and FIG. 7(C), comprises a Cylindrical Lens Array703 optically coupled to an Input Fiber 701, an Anamorphic Lens 705, afirst Polarization Beam Splitter (PBS) 707, Half-Waveplate (HWP) 709,Littrow Gratings 711 and 713, HWP 715, a second PBS 717, QWP 719,Rotationally Symmetric Lens 721, a Array of Programmable Mirrors 723, afirst Output Fiber 701-a, and a second Output Fiber 701-b. The device ofFIG. 7 may be mounted within an enclosure optimized for opticaltransmission, including a gas-filled enclosure, or the like.

Anamorphic Lens 705 and Rotationally Symmetric Lens 711 may be comprisedof multiple lens elements. It is well known in the art that lenses maybe comprised of multiple lens elements to achieve a particular opticalperformance. A prism may optionally be used in any embodiment of thesystem.

A multi-channel light signal 725 enters the device through the InputFiber 701, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 703. The Cylindrical Lens on the Cylindrical LensArray 703 collimates the multi-channel light signal 725 in the x-axisand directs it through the Anamorphic Lens 705. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Anamorphic Lens 705 collimates and focuses the multi-channel lightsignal 725 in the y-axis and directs it into the first PBS 707. The PBSseparates multi-channel light signal 725 into its s-polarized andp-polarized states.

The s-polarized optical component of Multi-channel light signal 725reflects off of the Beam Splitting Surface 708 of PBS 707 and exits PBS707. The s-polarized optical component then diffracts through LittrowGrating 713 and passes though HWP 715 which converts the s-polarizationstate to a p-polarized state. The p-polarized optical component ofMulti-channel light signal 725 transmits through the Beam SplittingSurface 708 of PBS 707, exits PBS 707, and passes though HWP 709 whichconverts the p-polarization state from p-polarized to s-polarized. Thiss-polarized light diffracts through Littrow Grating 711.

Grating 711 diffracts the individual Channels 727 and 729 (hereafterchannels) of the multi-channel light signal 725 into PBS 717. Grating713 diffracts the individual channels through HWP 715 which converts thes-polarization state to a p-polarized state.

Both the p-polarized and s-polarized states of the individual channelsenter second PBS 717; the s-polarized state reflects off of the BeamSplitting Surface 718 of PBS 717 and exits PBS 717. The p-polarizedstate transmits through the Beam Splitting Surface 718 of PBS 717, andexits PBS 717 recombined with the s-polarized state.

The individual channels are directed through QWP 719 and throughRotationally Symmetric Lens 721. The Rotationally Symmetric Lens 721focuses Channels 727 and 729 in both the x-axis and y-axis, near theProgrammable Mirror on the Mirror Array 723. More specifically,Rotationally Symmetric Lens 721 focuses Channel 727 near theProgrammable Mirror associated with Channel 727, and focuses channel 729near the Programmable Mirror associated with channel 729. By focusingthe channels in both the x-axis and y-axis, the optical beam size isreduced.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the two of Output Fibers 701-a or701-b. In this regard, each the channel is reflected back through thedevice in reverse and is directed toward that appropriate output fiber.In the presently detailed case of FIG. 7, the Programmable Mirrors areprogrammed so as to switch Channel 727 to Output Fiber 701-a and Channel729 to Output Fiber 701-b. The optical configuration is such that theoptical signals directed to and entering Output Fibers 701-a and 701 benter the Output Fibers within the cone of acceptance thereby reducingsystem loss. It will be clear to one skilled in the art that eitherChannel 727 or Channel 729 may be switched to either Output Fiber 701-aor 701-b by simply changing the angle of reflection of the associatedProgrammable Mirror. In this regard, the system may be scaled toaccommodate both a large number of Output Fibers, but also a largenumber of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, by receiving an opticalChannel 727 via Port 701-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port701.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 8(A), FIG. 8(B), FIG. 8(C), and FIG.8(D). FIG. 8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D). detail differentviews of the same device. It is of note that while only two channels areused in this example, a substantially larger number of channels andoptical ports may be employed. The wavelength selective optical switchallows for demultiplexing, multiplexing and switching separate opticalchannels to any one of a plurality of optical ports. The wavelengthselective optical switch of FIG. 8 may be dynamically programmed todemultiplex, multiplex and switch any combination of wavelengths to anyof a plurality of optical ports.

A first embodiment of the wavelength selective optical switch device ofFIG. 8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D) comprises FirstCylindrical Lens Array 803 optically coupled to an Input Fiber 801, aFirst Anamorphic Lens 805, a First Grating 807, a First RotationallySymmetric Lens 809, an Array of programmable Transmissive Beam Steerers(TBS) 810, a Second Anamorphic Lens 815, a Second Littrow Grating 817, aSecond Anamorphic Lens 815, a Second Cylindrical Lens Array 813, a firstOutput Fiber 811-a, and a second Output Fiber 811-b.

The device of FIG. 8 may be mounted within an enclosure optimized foroptical transmission, including a gas-filled enclosure, or the like.

The First and Second Cylindrical Lens Arrays 803 and 813, First andSecond Anamorphic Lenses 805 and 815, and First and Second RotationallySymmetric Lenses 809 and 819 may be comprised of multiple lens elements.It is well known in the art that lenses may be comprised of multiplelens elements to achieve a particular optical performance.

The Array of programmable TBS 810 is responsible for steering opticalsignals. However, other beam steering devices, such as a liquid crystalor the like, may also be employed. It will be clear to one skilled inthe art that beam steering devices may be used in any of the describedembodiments.

A prism may optionally be used in any embodiment of the system.Temperature changes cause grating to expand and contract. As gratingsexpand and contract the wavelength-sized gradations that causediffraction increase and decrease causing a change in the diffractionangle from a grating. As the temperature changes, the refractive indexof the prism changes, which in turn, changes the dispersion of theprism. Accordingly, a prism may be used to balance the thermal affectson the First and Second Gratings 807 and 817. When the prism andgratings are properly designed and configured the effects of temperatureon the system are greatly reduced. However, some embodiments of thesystem do not contain a prism.

A multi-channel light signal 821 enters the device through the InputFiber 801, and is directed through one of the Cylindrical Lenses on theFirst Cylindrical Lens Array 803. The Cylindrical Lens on the FirstCylindrical Lens Array 803 collimates the multi-channel light signal 821and directs it through the First Anamorphic Lens 805. When beam size islarge, the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The First Anamorphic Lens 805 collimates and focuses the multi-channellight signal 821 and directs it onto First Grating 807. The cylindricaland anamorphic lenses produce a beam with an elliptical footprint on thegrating. The major axis of the ellipse is perpendicular to the groovesso that the spectral resolution is maximized, while the overall size ofthe grating is less than that if a conventional rotationally symmetriccollimating lens were used.

First Grating 807 diffracts the individual Channels 823 and 825 of themulti-channel light signal 821 (hereafter channels) towards the FirstRotationally Symmetric Lens 809. The First Rotationally Symmetric Lens809 is preferably telecentric, so that the central ray, or chief ray, ofeach channel is parallel at the TBS plane. This minimizes the tiltrequired by the TBS. In a telecentric lens, the aperture stop is locatedat the front focus of the lens, resulting in the exit pupil being atinfinity. The First Rotationally Symmetric Lens 809 focuses the Channels823 and 825, in both the x-axis and y-axis, near the TBS Array 810. Morespecifically, Rotationally Symmetric Lens 809 focuses Channel 823 nearthe Programmable Mirror associated with Channel 823, and focuses channel825 near the Programmable Mirror associated with channel 825. Byfocusing the channels in both the x-axis and y-axis, the optical beamsize is reduced and the size of the TBS 810 may be reduced.

Depending upon the programmed state of the TBS 810, each channel may beswitched to any one of the two of Output Fibers 811-a or 811-b. In thisregard, each the channel is transmitted through the Second RotationallySymmetric Lens 819 which collimates the channels in both the x-axis andy-axis toward Second Grating 817. Second Grating 817 multiplexes thechannels switched to the same output fiber and diffracts the resultingbeam toward that output fiber. In the presently detailed case of FIG. 8,TBS 810 is programmed so as to switch Channel 823 to Output Fiber 811-aand Channel 825 to Output Fiber 811-b. Therefore, Channel 823 isdirected by its corresponding beam steerer on TBS 810 through SecondRotationally Symmetric Lens 819 which collimates the Channel towardsSecond Grating 817. Second Grating 817 diffracts Channel 823 throughSecond Anamorphic Lens 815. Second Anamorphic Lens 815 focuses Channel823 toward Second Cylindrical Lens 803, which focuses Channel 823 intoOutput Fiber 811-a. Similarly, Channel 825 is transmitted through SecondRotationally Symmetric Lens 819 which collimates the Channel towardsSecond Grating 817. Second Grating 817 diffracts Channel 825 throughSecond Anamorphic Lens 815. Second Anamorphic Lens 815 focuses Channel825 toward Second Cylindrical Lens 813, which focuses Channel 825 intoOutput Fiber 811-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 811-a and 811 b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 823 or Channel 825may be switched to either Output Fiber 811-a or 811-b by simply changingthe angle of direction of the associated TBS. In this regard, the systemmay be scaled to accommodate both a large number of Output Fibers, butalso a large number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, receiving an opticalChannel 813 via Port 811-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port801-a or 801-b.

A two channel grating-based optical switch, employing one embodiment ofthe invention, is detailed in FIG. 9(A), FIG. 9(B), FIG. 9(C), and FIG.9D). FIG. (A), FIG. 9(B), FIG. 9(C), and FIG. 9(D) detail differentviews of the same device. It is of note that while only two channels areused in this example, a substantially larger number of channels andoptical ports may be employed. This embodiment allows fordemultiplexing, multiplexing and switching separate optical channels toany one of a plurality of optical ports. This embodiment may bedynamically programmed to demultiplex, multiplex and switch anycombination of wavelengths to any of a plurality of optical ports.

The embodiment of the wavelength selective optical switch, detailed inFIG. (A), FIG. 9(B), FIG. 9(C), and FIG. 9(D), comprises a CylindricalLens Array 903 optically coupled to an Input Fiber 901, an AnamorphicLens 905, a Polarization Beam Splitter (PBS) 907, Littrow Gratings 911and 915, Faraday Rotators 909 and 913, QWP 916, Rotationally SymmetricLens 917, a Array of Programmable Mirrors 923, a first Output Fiber901-a, and a second Output Fiber 901-b. The device of FIG. 9 may bemounted within an enclosure optimized for optical transmission,including a gas-filled enclosure, or the like. The cylindrical andanamorphic lenses produce a beam with an elliptical footprint on thegrating. The major axis of the ellipse is perpendicular to the groovesso that the spectral resolution is maximized, while the overall size ofthe grating is less than that if a conventional rotationally symmetriccollimating lens were used.

Anamorphic Lens 905 and Rotationally Symmetric Lens 917 may be comprisedof multiple lens elements. It is well known in the art that lenses maybe comprised of multiple lens elements to achieve a particular opticalperformance.

A prism may optionally be used in any embodiment of the system.Temperature changes cause grating to expand and contract. As gratingsexpand and contract the wavelength-sized gradations that causediffraction increase and decrease causing a change in the diffractionangle from a grating. As the temperature changes, the refractive indexof the prism changes, which in turn, changes the dispersion of theprism. Accordingly, a prism may be used to balance the thermal affectson Gratings 911 and 915. Littrow Grating 911 and 915 may be opticallycoupled to one of the prism's surface. When the prism and Gratings 911and 915 are properly designed and configured the effects of temperatureon the system are greatly reduced. However, some embodiments of thesystem do not contain a prism.

QWP 916 may also be employed to reduce polarization dependent loss (PDL)in the system. QWP 916 oriented at 45 deg to the grating lines rotatesthe polarization of light traveling through the QWP so that light thatis s-polarized at the grating on the first pass is p-polarized on thesecond pass. The net result is no polarization dependent loss (PDL) forlight traveling between the Input Fiber 901 and any of the Output Fibers901-a and 901-b.

A multi-channel light signal 925 enters the device through the InputFiber 901, and is directed through one of the Cylindrical Lenses on theCylindrical Lens Array 903. The Cylindrical Lens on the Cylindrical LensArray 903 collimates the multi-channel light signal 915 in the z-axisand directs it through the Anamorphic Lens 905. When beam size is large,the geometrical limit holds and all the rays are parallel in acollimated beam. As the beam size decreases, diffraction becomesimportant and it is preferable to locate the beam waist at the Grating.The Anamorphic Lens 905 collimates and focuses the multi-channel lightsignal 915 in the y-axis and directs it into the PBS 907. The PBSseparates multi-channel light signal 925 into its s-polarized andp-polarized states.

Turning briefly to FIG. 10, the polarization states of multi-channellight signal 925 are described in detail. Multi-channel light signal 925strikes PBS 907 and the s-polarized optical component reflects, whilethe p-polarized component transmits through PBS 907. The s-polarizedcomponent of Multi-channel light signal 925 striking PBS 907 is notparallel to the y-axis, because the micro cylindrical collimators array901, 901-a, and 901-b are not in the xy-plane. The s-polarized opticalcomponent 925-SB passes through Faraday Rotator (FR) 909, which rotatesthe polarization state by 45 degrees such that the light 925-SG iss-polarized at the Littrow Grating 911. A Faraday rotator is anon-reciprocal optical device that rotates the polarization plane ofboth forward and backward transmitted beam in a certain direction,regardless of the transmission direction of the beam. Littrow Grating911 diffracts the individual channels 919-SG and 921-SG of light backthrough FR 909 that rotates the light a further 45 degrees so that thelight 919-PB and 921-PB is p-polarized in the reference frame of PBS907. Because individual channels 919-PB and 921-PB are now p-polarizedthey transmit through PBS surface 907 and exit the PBS 907, passingthough QWP 916 that converts the p-polarized light to left circularlypolarized light 919-LC and 921-LC.

Preferably, the input beam 925 at the PBS 907, and diffraction gratings911 and 915 are oriented such that the s-p coordinates at the gratingare rotated by 45 degrees from the s-p coordinates at the gratings. Forexample, in one embodiment, the incident beam makes a 51 degree anglewith the y-axis and is in the y-z plane and the PBS is rotated by 38degrees around the y-axis by 38 degrees. One skilled in the art willrecognize that many orientations of the incident beams 925, PBS, anddiffraction grating are possible.

In much the same fashion as described above with the s-polarized opticalcomponent, the p-polarized optical component 925-PB transmits throughPBS 907 and passes though FR 913 which rotates the polarization statefrom p-polarized in the reference frame of the PBS to s-polarized in thereference frame of the grating, and illuminates Littrow Grating 911.Littrow Grating 911 diffracts the individual channels of light backthrough FR 913 that converts their polarization to an s-polarized statein the reference frame of PBS 907, and into PBS 909. The s-polarizedoptical component 919-SB and 921-SB reflects off of PBS 907, passingthough QWP 916 that converts the s-polarized light to right circularlypolarized light 919-RC and 921-RC

Turning again to FIG. 9(A), FIG. 9(B), FIG. 9(C), and FIG. 9(D),Gratings 911 and 915 diffracts the individual Channels 919 and 921 ofthe multi-channel light signal 925 (hereafter channels) through PBS 907,QWP 916, and towards Rotationally Symmetric Lens 917. The RotationallySymmetric Lens 917 is preferably telecentric, so that the central ray,or chief ray, of each channel is parallel at the mirrors plane. Thisminimizes the tilt required by the MEMS mirrors. In a telecentric lens,the aperture stop is located at the front focus of the lens, resultingin the exit pupil being at infinity. The Rotationally Symmetric Lens 917focuses Channels 919 and 921 in both the x-axis and y′-axis (not shown),near the Programmable Mirror on the Mirror Array 923. More specifically,Rotationally Symmetric Lens 917 focuses Channel 919 near theProgrammable Mirror associated with Channel 919, and focuses channel 921near the Programmable Mirror associated with channel 921. By focusingthe channels in both the x-axis and y′-axis (not shown), the opticalbeam size is reduced.

Depending upon the programmed state of the Programmable Mirrors, eachchannel may be switched to any one of the two of Output Fibers 901-a or901-b. In this regard, each the channel is reflected back through theRotationally Symmetric Lens 917 which collimates the channels in boththe x-axis and y′-axis (not shown) and directs the channels through PBS907 and onto Gratings 911 and 913. Gratings 911 and 913 multiplex thechannels switched to the same output fiber and diffracts the resultingbeam toward that output fiber. In the presently detailed case of FIG. 9,the Programmable Mirrors are programmed so as to switch Channel 919 toOutput Fiber 901-a and Channel 921 to Output Fiber 901-b.

The optical configuration is such that the optical signals directed toand entering Output Fibers 901-a and 901-b enter the Output Fiberswithin the cone of acceptance thereby reducing system loss. It will beclear to one skilled in the art that either Channel 919 or Channel 921may be switched to either Output Fiber 901-a or 901-b by simply changingthe angle of reflection of the associated Programmable Mirror. In thisregard, the system may be scaled to accommodate both a large number ofOutput Fibers, but also a large number of channels.

It will be clear to one skilled in the art that the system may beoperated in the opposite direction. For example, by receiving an opticalChannel 927 via Port 901-a, multiplexing it with one or more receivedoptical channels, and directing the multiplexed optical signal via Port901.

1. A wavelength selective switch configured to couple with a pluralityof ports, the switch comprising: non-rotationally symmetric opticspositioned to receive light from a first of the plurality of ports, saidoptics configured to produce a substantially collimated non-rotationallysymmetric beam; a diffraction grating positioned to receive the beamfrom said optics; a lens positioned to receive at least a portion of thebeam from said diffraction grating; and a beam director array positionedto receive said at least a portion of the beam from said lens, said beamdirector array configured to direct said at least a portion of the beamthrough said lens to said diffraction grating, and from said diffractiongrating through said non-rotationally symmetric optics.
 2. Thewavelength selective switch of claim 1, wherein said non-rotationallysymmetric optics comprises an anamorphic lens.
 3. The wavelengthselective switch of claim 1, wherein said non-rotationally symmetricoptics comprises a cylindrical lens.
 4. The wavelength selective switchof claim 1, wherein said non-rotationally symmetric optics comprises acylindrical lens and an anamorphic lens.
 5. The wavelength selectiveswitch of claim 1, wherein the non-rotationally symmetric beam has across-section transverse to the direction of propagation of the beamhaving the shape of an ellipse, said ellipse having major and minoraxes.
 6. The wavelength selective switch of claim 5, wherein saiddiffraction grating comprises a plurality of grooves, each groove ofsaid plurality of grooves being elongated along a first direction, saidmajor axis of said ellipse oriented along a second direction that issubstantially perpendicular to the first direction along which saidplurality of grooves is elongated.
 7. The wavelength selective switch ofclaim 1, wherein said optics and said diffraction grating define anoptical path therebetween, said non-rotationally symmetric beam beingelongated along a direction perpendicular to said optical path betweensaid optics and said diffraction grating.
 8. The wavelength selectiveswitch of claim 1, wherein said diffraction grating operates at Littrow.9. The wavelength selective switch of claim 1, wherein said lens isrotationally symmetric.
 10. The wavelength selective switch of claim 1,wherein said beam director array is programmable among a plurality ofstates.
 11. The wavelength selective switch of claim 1, wherein saidbeam director array directs said at least a portion of the beam to asecond of the plurality of ports when in one state, and directs said atleast a portion of the beam to a third of the plurality of ports when inanother state.
 12. The wavelength selective switch of claim 1, whereinsaid beam director array is electrically programmable.
 13. Thewavelength selective switch of claim 1, wherein said beam director arraycomprises a MEMS mirror.
 14. The wavelength selective switch of claim 1,wherein said non-rotationally symmetric beam is substantially collimatedalong a first axis and a second axis.
 15. The wavelength selectiveswitch of claim 1, wherein said non-rotationally symmetric beam iselongated along said first axis.
 16. The wavelength selective switch ofclaim 1, wherein said first axis is perpendicular to said second axis.17. The wavelength selective switch of claim 1, wherein said first axisis a major axis and said second axis is a minor axis.
 18. The wavelengthselective switch of claim 1, wherein said beam defines an ellipse.